1. Field of the Invention
This invention relates to devices for lowering heavy loads along a suspended cable from an elevated location and particularly relates to fire escape devices. The invention especially relates to controlled-velocity escape devices which are selectively attached to a building or descend with a passenger.
2. Review of the Prior Art
Devices for safe passage down a flexible tensional support means, such as a rope or cable, that is attached to an elevated object, such as the top of a building, a cliff, or a mine shaft, have been known for many centuries. Safe descent in such devices has required control of the speed of descent and has been provided by subjecting the cable to great pressure over a limited area of contact, by frictionally engaging the cable over an extended area of contact with relatively light pressure, or by utilizing a braking means, such as a winch having a spring-controlled ratchet wheel. Examples among early United States patents of these three types are, respectively, U.S. Pat. Nos. 387,772, 496,923, and 643,286. Speed control has been imparted by pre-setting a braking means according to the weight of the passenger at the beginning of the descent, by manipulating a passenger-operated braking means that is under control of the passenger during the descent, or by using an automatically operating braking means that is responsive to the weight of the passenger or other load. Examples among United States patents of these three types are, respectively, U.S. Pat. Nos. 643,286, 481,923, and 854,922. Devices utilizing relatively light pressure over an extended area of contact generally provide a tortuous, serpentine, or sinusoidal path of travel for the cable and achieve speed control, whether with a passenger-operated means or with a weight-responsive means, by varying the area of contact or the pressure exerted upon the cable in accordance with the weight of the load, examples being respectively, U.S. Pat. Nos. 876,840 and 835,180.
Varying the area of contact has usually involved changing the total arc of contact of the cable with a frictional surface such as a pulley or roller, such as by moving the center-to-center distance apart between the rollers in a single series of rollers around which the cable is sinusoidally wound or by moving the rollers in a pair of parallel series into greater or lesser proximity, examples being, respectively, U.S. Pat. Nos. 3,739,875 and 876,840.
These devices, notwithstanding their variety, are apparently adapted for merely a single type of installation and usage, such as being fastened to a building (an example being U.S. Pat. No. 854,922) or moving with the escaping passenger (an example being U.S. Pat. No. 3,739,875). Both physical strength and presence of mind are needed for controlling speed of descent in the devices having levers and the like to be operated by a passenger. Clearly, frightened elderly persons are incapable of using such devices, as when escaping from a burning building, so that they are unsafe for these people.
Fire-escape devices as discussed hereinbefore have not been generally adopted because of high cost, large size, awkwardness in handling, and necessity for passenger operation to control speed of descent. An automatically weight-responsive device that is light, simple to construct, reliable, and versatile as to installation and usage is clearly needed for enabling one or many people to escape from upper floors of burning buildings and for lowering people and equipment during mining operations, mountain climbing, cave exploring, and construction activities, for example.